There is a communication protocol of a wireless relay scheme that is applied to a digital wireless-relay communication system using random access as a basic media access control scheme.
For example, a communication protocol of a wireless relay scheme reported in Non-patent Document 1 is based on Association of Radio Industries and Businesses (ARIB) standard STD-T67, which is a standard protocol for a specified low-power radio. An example of a configuration of a wireless relay system and time-slot control of packets in accordance with this conventional example is illustrated in FIGS. 16 and 17.
When transmitting a packet, a transmission station senses a carrier before transmission. At this time, if the carrier has been detected, the transmission station returns to a waiting state. If no carrier has been detected, the transmission station acquires a time to be set in a transmission delay timer using a random number, sets the acquired time in the transmission delay timer, and waits for the timer to time out. If the transmission station has detected the carrier while waiting for the time-out, the transmission station returns to a waiting state. If there is no carrier and the transmission delay timer has timed out, the transmission station initiates packet transmission. In order to secure the reliability of the packet transmission, the transmission station waits for an ACK signal from a partner station. If no ACK signal has been received after the transmission station has waited for a defined time, the transmission station transmits a packet signal up to 7 times. Such a media access control scheme is referred to as a carrier sense multiple access with collision avoidance (CSMA/CA) scheme, and is adopted in the Institute of Electrical and Electronics Engineers (IEEE) 802.11 wireless local area network (LAN) standard, which is a wireless LAN standard. In communication indicated by a two-way arrow in FIG. 16, random access is performed in accordance with CSMA/CA.
It is to be noted that this conventional scheme does not employ network encoding technology for improving system throughput.
In addition, a communication protocol of a wireless relay scheme reported in Non-patent Document 2 adopts a time-division multiple access (TDMA) scheme, which is a scheme that manages a schedule with respect to time slots in a time domain. An example of a configuration of a wireless relay system and time-slot control of packets in accordance with this conventional example is illustrated in FIGS. 18 and 19. This scheme is a wireless relay scheme in which an influence of propagation of radio waves between terminal stations and relay stations is considered, a deployment distance between the respective stations is considered so that the ratio waves of the respective stations do not interfere with each other, time slots to be used by the respective stations are temporally separated when packet collision occurs, and stations that are positioned at sufficiently distant locations are permitted to transmit packets with the same frequency at the same time. In communication indicated by a two-way arrow in FIG. 18, access scheduled in accordance with TDMA is performed.
It is to be noted that this conventional scheme employs network encoding technology for improving system throughput.